The invention relates generally to power converters and more specifically to a multilevel converter.
In the last few decades, the field of power conversion has grown tremendously due to its imminent advantages in motor drives, renewable energy systems, high voltage direct current (HVDC) systems, and the like. For example, a subsea oil and gas production system which requires hundreds of megawatts of electric power may employ a HVDC transmission and distribution system for delivery of electric power. Such HVDC systems typically include a land-based or topside converter substation where the AC-to-DC power conversion is performed. The multilevel converter is emerging as a promising power conversion technology for such medium and high voltage applications.
Multilevel converters offer several advantages over ordinary two-level converters. For example, the power quality of the multilevel converter is better than that of two level converters. Also, the multilevel converters are ideal for interface between a grid and renewable energy sources such as photovoltaics (PV), fuel cells, wind turbines, and the like. In addition, the efficiency of the multilevel converter is relatively higher as a result of its minimum switching frequency.
In the recent times, the multilevel converters having a modular structure and without transformers have been designed. The modular structure of the converters, allows stacking of these converters to an almost unlimited number of levels. Also, the modular structure aids in scaling up to different power and voltage levels. However, certain currently available multilevel converters such as modular multilevel converters (MMC) typically employ a large number of fully controllable semiconductor switches, such as insulated gate bipolar transistors (IGBTs).